At the right corner of the dash, facing the door, the panel pulls off best with a plastic tool, but a screwdriver works well also. There are plastic clips on that panel that pop in and out easily. Push in on the front of that panel, and toward the rear it will move out. Slip the tool in there.
Behind that, near the top is a 1/2" hole filled with spray foam. Push a coat hanger thru in the center of the hole, with the wires taped to it. Can go directly to the battery there. I just finished that on my 2014 Rubicon.
I put the wires inside plastic wireloom up to the hole, and at the other side, to the battery. Also a fuse by the battery.
Then you will have clean power without ripples or sounds from relays, ect.
Or you could ground just below the hole inside the cabin. There is a bolt there, put a washer over the wire, so as not to cut it on the bolt head.